Forty years after his death, the militant marxist continues to divide left-wingers around the world. Here, two prominent thinkers debate El Comandante's legacy.

George Galloway: Yes

From Caracas to Cape Town, Chesterfield to Cowdenbeath, one man's admittedly handsome face on a T shirt tells you more about its wearer than how well he or she fits it. Ernesto "Che" Guevara, who was murdered by United States agents under orders from Washington 40 years ago, is the face of global rebellion.

He inspires all the more intensely since he could have lived a prosperous bourgeois life as an Argentine dentist. Instead, and despite asthma, he chose a life of action, a motorcycle diarist, a comandante in a triumphant Cuban revolutionary army, a guerrilla leader in the Congo, a martyr in the mountain gulleys of Bolivia.

It's true he had a spell as a bank manager – but it was the governorship of Cuba's revolutionary state bank.

It was the 1950s motorcycle tour that did it. The immiserated wastelands of Latin American, where the poor starved, the latifundists larked and the US corporations sucked the blood of South America.

In 1954 he witnessed the overthrow of the reforming Guatemalan government at the behest of the United Fruit company, run by those scions of the US establishment, the Dulles family.

By the time Che Guevara met Fidel Castro a year later he was a rebel. After, he was a revolutionary. Guevara had absolutely no military background and signed on with Fidel as the rebel "army's" doctor. In the mountains of eastern Cuba in the late 1950s he became a military leader and a strategist of revolutionary warfare of the first order. It was an old-fashioned ethos: lead your men (and women) from the front and don't ask them to do anything you aren't prepared to do with them.

It was in no small measure due to his military victories that the Cuban revolution triumphed – the rebels' entry into Havana on New Years Day 1959 is memorably recreated in the Godfather II. The Mafiosi and the bordello owners headed for the airport with the barbaric dictator Fulgencio Batista.

Those who would traduce Che, Fidel and the Cuban revolutionaries must say what Cuba would be like now if that dictatorship had held on – Haiti, the most hellish place in the Western hemisphere is literally not far from Cuba, but metaphorically in a different universe.

By the standards of Cuba's blood-drenched history the retribution visited on the dictator's henchmen was light – even according to the US ambassador to Havana and the head of the CIA at the time, Alan Dulles.

Che, in particular, defies the right-wing stereotype of the ice-cold, cunning revolutionist. He said that 'the true revolutionary is guided by a great feeling of love. It is impossible to think of a genuine revolutionary lacking this quality.'

Even as Cuba, in the grip of the US's embargo, looked to the Soviet Union for support, Che was prepared to criticise the bureaucratism he saw in Moscow.

It's a staple of liberal and conservative cynics that revolutionaries such as Che ineluctably end up mirror images of the monsters they set out to overthrow. No one shatters that lazy cliché more than Che.

Instead of settling down in Havana, he set out to spread revolution in Congo, where the great Patrice Lumumba had been murdered in a UN-supported coup. Nelson Mandela paid tribute to the Cuban role in Africa's liberation struggle. On his release from prison he went to Cuba, rather than any other capital in the world, beneath an illumination of Che's image, Mandela lifted his hands aloft and said: 'See how far we slaves have come!'

'There are no frontiers in this struggle to the death,' Che told an international conference in 1965. 'We cannot remain indifferent in the face of what occurs in any part of the world. A victory for any country against imperialism is our victory, just as any country's defeat is our defeat.'

That internationalism, which has become a leitmotif of today's movements, connected him with the masses on every continent.

Even the coldest of latter-day Cold Warriors must have been moved by the recent story that a Cuban medical team last year saved the sight of Mario Teran, the Bolivian sergeant who executed Che.

One of the greatest mistakes the US state ever made was to create those pictures of Che's corpse. Its Christ-like poise in death ensured that his appeal would reach way beyond the turbulent university campus and into the hearts of the faithful, flocking to the worldly, fiery sermons of the liberation theologists.

Which leaves the liberals, who say that they too, as Che put it, '. . . tremble with indignation at every injustice,' but who turn up their noses when the despairing mass of people resort to force against the daily violence of the elite.

They call to mind the admonition of the great black abolitionist Frederick Douglass: 'Those who profess to favour freedom and yet depreciate agitation... want the ocean without the awful roar of its many waters.... Power concedes nothing without a demand.'

Today, a new generation is struggling for progress – drawing strength from Hugo Chavez's Bolivarian revolution, while many of us also remain mindful of the catastrophe that engulfed Allende and the Chilean movement when those who stood in its way were not defanged. To wish Venezuela's social reforms without Che's revolutionary steadfastness is to will the first 11 September atrocity – Santiago, Pinochet, 1973, gunfire drowning the song of a new Chile.

Che's time is not past – it is coming. I was struck recently by the remarkable introduction by Lucia Alvarez de Toledo to a compilation of Che's Bolivian diaries. She met the daughter of the telegaphist in the Bolivian village where Che was taken who had communicated the first written word of his murder.

Toldeo writes: "She said she had been there when Guevara had died. She said she was 19 at the time. Then she cast a look around her and said, 'Look at us. Nothing has changed since then. El Commandante came too soon. We were ignorant and did not understand him... We abandoned him... and here we are just as we were before he came, or maybe even worse.' "

Johann Hari: Should Che be an icon? No

The myth of Che Guevara is seductive and lush. It's the story of an Argentinian rich-boy who was so shocked by poverty he became a Robin Hood fighting alongside the poor, until eventually he was murdered by the CIA. But the reality of Che Guevara is very different. The facts show that he was a totalitarian with a messiah streak, who openly wanted to impose Maoist tyranny on the world. He was so fanatical that at the hottest moment in the Cold War, he even begged the Soviet Union to nuke New York or Washington or Los Angeles and bring about the end of the world.

It is true that Che's story begins with a motorcycle journey across South America. The young man was repulsed by the gap between the swanky transplanted European culture in which he lived and the starving misery of the indigenous peoples. He could see that this was caused largely by America's habit of smashing local governments and replacing them with dictators prepared to slobber over US corporations. But he concluded from that journey – gradually, over a few short years – that there was only one solution: the imposition of authoritarian communism, by force, everywhere. He chose not to see that this system, wherever it is tried, makes people even poorer still, invariably spreading famine, starvation, and terror.

Since the Soviet Union was too soft for his tastes, there were only two countries that Che found truly admirable: Maoist China and Kim Il Sung's North Korea. He bragged that there was "not a single discrepancy" between Mao's world view and his own. As Che was happily fawning over Mao in the flesh in Beijing, in the surrounding countryside there was an epidemic of mothers cutting off the flesh from their inner thighs to feed it to their starving children. The programme that caused this biting hunger – the mass collectivisation of the farms – represented "true socialist morality", Che said. The dictator killed 70 million people in the end, cheered on by his guerrilla friend at every stage.

Of course, Che's defenders act as if this was the only choice confronted by Latin Americans: you were either for US-imposed market fundamentalism, or for Maoist Communism. But you don't have to look very far in Che's life to see that this is a lie. His diaries show that he was constantly appalled to discover that almost everyone around him, including the revolutionaries fighting by his side, did not share his Maoist vision for the future. His first wife, Hilda Gadea, was a social democrat. She wanted to depose the US-backed tyrants – and then replace them with moderate, Swedish-style mixed economies. Che ridiculed and pilloried her as "bourgeois", before abandoning both her and their child. The ordinary Cubans he fought alongside on the Sierra Maestre also wanted to create a democracy with a mixed economy. Disgusted, Che noted in his diary: "I discovered the evident anti-communist inclinations of most of them."

When Che and Fidel Castro's guerrilla army seized power in Cuba, he was immediately – and to his delight – put in charge of the firing squads. He instituted a system of 'trials' that lasted just a few hours, with himself as sole judge. They invariably ended with the low-level functionaries of the Batista regime being lined up and shot. Che's public declarations from that time are blunt. "All right, it is dictatorship," he shouted at one point. "It's criminal to think of the needs of the individual." He even banned Santa Claus, saying he was an "American imperialist import."

The friend who had travelled with Che on the famous motorcycle journeys, David Mitrani, was shocked when they met up in Havana after the revolution. He could not understand how Che's compassionate response to poverty all those years ago had led him to announce he now wanted to become an " effective, violent, selective, and cold killing machine".

Che's fanaticism reached its peak in October 1963, when he seriously advocated a course of action that would immediately end life on earth. Che had implored the Soviet Union to place nuclear missiles on Cuba. He knew the US would interpret this as an act of aggression and probably retaliate with nuclear weapons – but he said that "the people [of Cuba] you see today tell you that even if they should disappear from the face if the earth because an atomic war is unleashed in their names... they will feel completely happy and fulfilled" knowing the revolution had inspired people for a while. Che did not say how he knew the Cuban people would be delighted to die of radiation sickness, their hair burning on their heads and their skin slopping from their faces.

The Soviet Union followed Che's advice – and the world came closer to nuclear annihilation than at any point before or since. On the American side, maniacs like General Curtis LeMay implored Jack Kennedy to nuke Moscow immediately. On the Soviet side, Che Guevara played exactly the same role. He urged Khrushchev to launch a nuclear strike, now, against US cities. For the rest of his life, he declared that if his finger had been on the button, he would have pushed it. When Khrushchev backed down and literally saved the world, Che was furious at the "betrayal". If Che's recommendations had been followed, you would not be reading this newspaper now.

None of these facts are seriously disputed by historians; they are simply skidded over by Che's defenders, who stick to romantic generalities about how he stood for "honesty" and "revolution". But Che Guevara is not a free-floating icon of rebellion. He was an actual person who supported an actual system of tyranny, one that murdered millions more actual people.

If the small lingering band of communo-nostalgists who still revere Che were honest about continuing his life's work, they would have to form a group called "Left-Wingers for Creating a Universal North Korea, Prior to Universal Death in a Nuclear Winter." I don't think they would find many recruits.